Processes for the production of alkyl boric acid esters and free alkyl boric acids



United States Patent 2,992,267 PROCESSES FOR THE PRODUCTION OF ALKYLgggC ACID ESTE'RS AND FREE ALKY'L BORIC S Roland Kiister, Mulheim(Ruhr), Germany, assignor to Studiengesellschaft Kohle m.b.H., Mulheim(Ruhr), Germany, a corporation of Germany 'No Drawing. Filed Oct. 21,1958, Ser. No. 768,577 Claims priority, application Germany Oct. 23,1957 '16 Claims. (Cl. 260-462) This invention concerns processes for theproduction of alkyl boric acid esters and free alkyl boric acids.

'It has long been known to obtain alkyl boric acid esters of the generalformula RB(OR) in which R represents a hydrocarbon radical, by the useof alkylation agents, such as for example Grignard compounds or zincalkyls, from boric acid esters of the general formula B(OR) in which Ris likewise a hydrocarbon radical. Alkyl boric acid esters have alsobeen successfully produced by the oxidation of boron trialkyls using dryair. In this case one or two alkyl groups on the boron atom aretransformed into the corresponding alkoxy groups.

Since boron trialkyls of the general formula BR in which R represents analiphatic hydrocarbon radical, can in these days easily be obtained bysimple manufacturing processes, more especially by using aluminiumtrialkyls, these aliphatic boron hydrocarbons BR are also suitable froman economic point of view for further processing to produce alkyl boricacid esters or free alkyl boric acids. The manufacture of alkyl boricacid esters by oxidation, likewise starting from the boron trialkyls, isuneconomical because of the loss of one or two valuable alkyl groups.

It has now been found to be possible to manufacture alkyl boric acidesters from boron trialkyls in a very simple manner while maintainingall boron-carbon bonds therein. The present invention is concerned withthe reaction of boron trialkyls with boric acid esters to form alkylboric acid esters in good yields in accordance with the followinggeneral equations:

in which R and R represent hydrocarbon radicals which can be the same ordifierent.

The reaction according to the invention was not in any way to beexpected since, according to the data given in technical literature,previously experiments which were to have led to the reaction of boronalkyls with boric acid esters produced negative results (cf. H.Meerwein, H. Stinke, J. Pr. Chem. 147, 252 (1936)). This reaction can,however, easily be carried out successfully in accordance with theinvention.

According to the invention, a boron trialkyl of the general formula BRin which R represents an aliphatic hydrocarbon radical, is heated with aboric acid ester of the general formula B(OR') in which R represents analiphatic hydrocarbon radical, to a temperature exceeding 100 C., andadvantageously to 200 C. or higher. Irrespective of the molar ratiowhich is emout the process, this is generally shown by a correspondinglysmaller conversion of the boron alkyl to monoalkyl boric acid ester.With an excess of boric acid ester in relation to the boron trialkyl theexcess quantity of boric acid ester is recovered, in addition to thealkyl boric acid ester. Advantageously, for the production of amonoalkyl boric acid ester, a mixture of 1 mol of a boron trialkyl isheated with 2 mols of a boric acid ester, possibly in a pressure vessel,to temperatures between 200 and 250 C., the corresponding monoalkylboric acid ester being formed in a substantially quantitative yield. Asubsequent distillation is not absolutely necessary.

When carrying out the process according to the invention, it isadvisable to work without solvents so that the alkyl boric acid estercan be obtained directly in a pure form. It is, however, possible to usecertain solvents. All saturated aliphatic and aromatic hydrocarbons aresuitable for this purpose and it is possible to use ethers as solvents.The use of solvents is particularly advisable when using solid startingmaterials or when solid products are formed.

From the alkyl boric acid esters which can be producedby the process ofthe invention, it is possible to obtain the free alkyl boric acids in aknown manner by reaction with water. The B-alkyl boroxols are formedfrom the monoalkyl boric acids by splitting-off water. Alkyl boric acidesters are of importance as additives to engine fuels.

. The following examples further illustrate the invention:

A mixture of 70 g. (0.5 mol.) of boron tri-n-propyl and 104 g. (1 mol)of trimethyl borate is placed under nitrogen in a 500 cc. autoclave,which is heated while shaking for 23 hours at 250 C., pressures up to amaximum of 30 atm. being reached. After cooling, the colourless liquidis emptied out. By distillation, and after a small quantity of firstrunnings, 150 g. of monopropyl boric acid dimethyl ester with a boilingpoint of 102- 103 C. are obtained. The benzoic peracid value of thecompound corresponds to that of one alkyl group on the boron.

A mixture of 175 g. (0.5 mol) of pure boron tri-noctyl and 292 g. (2.0mol) of triethyl borate is heated for 10 hours at 200 C. in a l-litreautoclave. The colourless discharged is thereafter distilled. 150 g. ofunmodified triethyl borate (B.P. 16/17 mm.=2930 C.) are ployed, amonoalkyl boric acid ester is generally formed.

The dialkyl boric acid monoalkyl ester formed in the first stage of thereaction is generally further converted with disproportionation underthe conditions of the reaction, in accordance with the equation:

so that in such cases unconverted trialkyl boron is left as well as amonoalkyl boric acid ester. Consequently, if the quantity of boric acidester is too low when carrying obtained as first runnings. The monooctylboric acid diethyl ester which is formed boils at 7075 C. under apressure of 2 mm. Hg. A total of 230 g. (=72% of the theoretical) isobtained. The benzoic peracid value of the compound indicates aboron-carbon bond in the molecule.

Example 3 of n-hexyl boric acid diethyl ester (M.P.=48 C.)

n =1.4084, are obtained. After a small quantity of intermediate runnings(about 5 g.) unreacted tri-n-hexyl boron is left as residue.

2,992,2e7 i r I g 4 Example 4 Example 8 z s) s -l- G 13)3='( Z 5) 2 61a) C H B(OOH 2 z 5) e ia)2 343.5 g. (0.5 mol) of boron-tri-n-hexadecyl(M.P.

62.4 g. (0.198 mol) of tri-n-hexyl borate and 42.8 g. (0.437 mol) ofboron triethyl are heated for 10 hours at 230240 C. in a 200 cc.autoclave. The liquid (103 g.) is emptied out and distilled in a column,the following fractions being obtained:

(1) 15.5 cc. of unreacted boron triethyl (B.P.

(2) B.P. =6970/1 C.; 53 cc. of diethyl boric acid hexyl ester.

(3) B.P. =20-63 C.; 1.5 cc. of intermediate runnings.

(4) B.P. =63-65 C.; 40 cc. of monoethyl boric acid di-n-hexyl ester.

Example 5 73.6 g. (0.277 mol) of boron tri-n-hexyl and 20.1 g. (0.137mol) of triethyl borate are heated for about 6-7 hours at 240 C. in aclosed vessel. The discharged liquid is distilled under reduced pressureand the following fractions are obtained:

(3) B.P.0' 7 0 03 6264 C.; CC. of di-n-hexyl bOI'iC acid monoethyl esterwith a melting point (indefinite) of 58 to -4S C.

(4) A residue consisting mainly of unreacted trihexyl boron (55 cc.).

From the first two fractions, on being redistilled with the use of ahighly effective column, monohexyl boric acid diethyl ester of B.P.=89-90 C. (M.P.=-48 C.; n =l.4084) is obtained in pure form after asmall quantity of first runnings.

Example 6 OH: CaH'IB l 202 g. (1 mol) of a glass-like boric acid glycolester (prepared from 70 g. of boron trioxide and 186 g. of anhydrousglycol) are mixed with 200 g. (1.43 mol) of boron tri-n-propyl. Themixture is heated and, with an internal temperature of 140-160 C.(reflux), the boric acid ester gradually dissolves in the boron alkyl. Acolourless liquid (B.P.=126-130 C.) distils into the receiver. 'Finally,all the liquid is distilled 0E under reduced pressure and no residue isleft. The liquid is rectified in a 40 cm. filler body column. After asmall quantity of first runnings, 278 g. (about 300 cc.) of puremono-n-propyl boric acid glycol ester (B.P.=127 C., B.P. =85 C.; n='1.4054, d =0.9225) with a boron content of 9.5% are obtained. 70 g. ofunreacted boron tripropyl are recovered.

Example 7 1O 21 3)2 434 g. (1 mol) of boron tri-n-decyl are heated for4-5 hours with 260 g. (2.5 mols) of trimethyl borate to 240-280" C. in a1 litre autoclave. A colourless liquid is obtained, the distillation ofwhich yields mono-ndecyl boric acid dimethyl ester (B.P. =125-130 C;B.P. =5152 C., n =1.4246, d =0.8398), after first runnings (70 g. ofexcess trimethyl borate of B.P. =68-69 C.). As residue, 40 g. ofunreacted boron-ndecyl are obtained. With quantitative yield, theconversion to mono-n-d'e'cyl boric acid dimethyl ester (575 g.) amountsto 90% of the theoretical.

=28-30" C.) are dissolved in 200 cc. of hexane; 130 g. of trimethylborate are added to this solution. The mixture is heated in a l-litreautoclave for 6 hours at 220- 240 C. After cooling and distilling offthe solvent together with the excess trimethyl borate, a colourlessreadily mobile liquid is obtained, the distillation of which, underreduced pressure (B.P. =l05106 C.), produces 375 g. (85% conversion withquantitative yield) of mono-n-hexadecyl boric acid dimethyl ester, n=1.4378, d =0.8349. The residue (50 g. of boron tri-n-hexadecyl)solidifies slowly on cooling.

for 6 hours at 220-250" C. After cooling, the excess trimethyl borate isdistilled off together with the solvent.

. Under reduced pressure, 185 g. (80% conversion with quantitativeyield) of monocyclohexyl boric acid dimethyl ester (B.P. =70-71 C. n=l.4359, r1 =0.9183) are obtained.

What I claim is:

1. Process for the production of alkyl boric acid esters which comprisesheating a boron trialkyl of the general formula BR wherein R representsa saturated aliphatic hydrocarbon radical with a boric acid esterselected from the group consisting of boric acid glycol esters andesters of the general formula B(OR') wherein R represents a saturatedaliphatic hydrocarbon radical, which radical may be the same as thesaturated aliphatic hydrocarbon radical designated R, to a temperaturein excess of C. and recovering said alkyl boric acid ester.

2. Process according to claim 1, which comprises efiecting the heatingat a temperature in excess of 200 C.

3. Process according to claim 1, which comprises heating 1 rnol of saidboron trialkyl with 2 mols of said boric acid ester to from 200 to 250C.

4. Process according to claim 1, which comprises subjecting saidreaction mixture following said heating to distillation.

5. Process according to claim 1, which comprises, in those instanceswhere at least one component of the reaction mixture is a solid,effecting the reaction in the presence of a solvent.

6. Process according to claim 5, wherein said solvent-is a memberselected from the group consisting of aliphatic hydrocarbons, aromatichydrocarbons and ethers.

7. Process according to claim 1, which comprises effecting the reactionin a pressure vessel.

8. Process according to claim 1, wherein the compound designated BR isboron tri-n-propyl and the compound designated B(OR) is trimethylborate.

9. Process according to claim 1, wherein the compound designated ER, isboron tri-n-octyl and the compound designated B(OR') is triethyl borate.

10. Process according to claim 1, wherein the compound designated BR isboron tri-n-hexyl and the compound designated B(OR') is triethyl borate.

11. Process according to claim 1, wherein the compound designated BR isboron triethyl and the compound designated B(OR) is tri-n-hexyl borate.

12. Process according to claim 1, wherein the compound designated BR isboron tri-n-propyl and said ester is boric acid glycol ester.

13. Process according to claim 1, wherein the com- 5 pound designated BRis boron tri-n-decyl and the compound designated B(OR) is trimethylborate.

14. Process according to claim 1, wherein the compound designated BR isboron tri-n-hexadecyl and the compound designated B(OR') is trirnethylborate.

15. Process according to claim 1, wherein the compound designated BR isboron tricyclohexyl and the compound designated B(OR') is trimethylborate.

16. Process for the production of alkyl boric acid esters capable ofconversion by hydrolysis to free alkyl boric 10 2,835,693

acids which comprises heating a boron trialkyl having the generalformula BR in which R represents a saturated aliphatic hydrocarbonradical with a boric acid ester selected from the group consisting ofboric glycol esters and esters of the general formula B(OR) in which R15 6 represents a saturated aliphatic hydrocarbon radical which may bethe same as the saturated aliphatic hydrocarbon radical designated R, toa temperature in excess of 100 C. to thereby form a boric acid estercapable of hydrol- 5 ysis to form the free acid.

References Cited in the file of this patent UNITED STATES PATENTS Bulset al May 20, 1958 OTHER REFERENCES Lappert: Chem. Reviews, vol. 56, p.985 (1956). (Copy in Scientific Library.)

1. PROCESS FOR THE PRODUCTION OF ALKYL BORIC ACID ESTERS WHICH COMPRISESHEATING A BORON TRIALKYL OF THE GENERAL FORMULA BR3, WHEREIN RREPRESENTS A SATURATED ALIPHATIC HYDROCARBON RADICAL WITH A BORIC ACIDESTER SELECTED FROM THE GROUP CONSISTING OF BORIC ACID GLYCOL ESTERS ANDESTERS OF THE GENERAL FORMULA B(OR'')3, WHEREIN R'' REPRESENTS ASATURATED ALIPHATIC HYDROCARBON RADICAL, WHICH RADICAL MAY BE THE SAMEAS THE SATURATED ALIPHATIC HYDROCARBON RADICAL DESIGNATED R, TO ATEMPERATURE IN EXCESS OF 100* C. AND RECOVERING SAID ALKYL BORIC ACIDESTER.